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<span class="breadcrumb-node">取回一个文档</span>
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<div class="titlepage"><div><div>
<h2 class="title">
<a id="get-doc"></a>取回一个文档<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elasticsearch-cn/elasticsearch-definitive-guide/edit/cn/030_Data/15_Get.asciidoc">edit</a>
</h2>
</div></div></div>
<p>为了从 Elasticsearch 中检索出文档，我们仍然使用相同的 <code class="literal">_index</code> , <code class="literal">_type</code> , 和  <code class="literal">_id</code> ，但是 HTTP 谓词更改为 <code class="literal">GET</code> :</p>
<div class="pre_wrapper lang-sense">
<pre class="programlisting prettyprint lang-sense">GET /website/blog/123?pretty</pre>
</div>
<div class="sense_widget" data-snippet="snippets/030_Data/15_Get_document.json"></div>
<p>响应体包括目前已经熟悉了的元数据元素，再加上  <code class="literal">_source</code> 字段，这个字段包含我们索引数据时发送给 Elasticsearch 的原始 JSON 文档：</p>
<div class="pre_wrapper lang-js">
<pre class="programlisting prettyprint lang-js">{
  "_index" :   "website",
  "_type" :    "blog",
  "_id" :      "123",
  "_version" : 1,
  "found" :    true,
  "_source" :  {
      "title": "My first blog entry",
      "text":  "Just trying this out...",
      "date":  "2014/01/01"
  }
}</pre>
</div>
<div class="note admon">
<div class="icon"></div>
<div class="admon_content">
<p>在请求的查询串参数中加上 <code class="literal">pretty</code> 参数，正如前面的例子中看到的，这将会调用 Elasticsearch 的 <em>pretty-print</em> 功能，该功能 使得 JSON 响应体更加可读。但是， <code class="literal">_source</code> 字段不能被格式化打印出来。相反，我们得到的 <code class="literal">_source</code> 字段中的 JSON 串，刚好是和我们传给它的一样。</p>
</div>
</div>
<p><code class="literal">GET</code> 请求的响应体包括 <code class="literal">{"found": true}</code> ，这证实了文档已经被找到。 如果我们请求一个不存在的文档，我们仍旧会得到一个 JSON 响应体，但是  <code class="literal">found</code> 将会是 <code class="literal">false</code> 。
此外， HTTP 响应码将会是 <code class="literal">404 Not Found</code> ，而不是 <code class="literal">200 OK</code> 。</p>
<p>我们可以通过传递 <code class="literal">-i</code> 参数给 <code class="literal">curl</code> 命令，该参数能够显示响应的头部：</p>
<div class="pre_wrapper lang-sh">
<pre class="programlisting prettyprint lang-sh">curl -i -XGET http://localhost:9200/website/blog/124?pretty</pre>
</div>
<p>显示响应头部的响应体现在类似这样：</p>
<div class="pre_wrapper lang-js">
<pre class="programlisting prettyprint lang-js">HTTP/1.1 404 Not Found
Content-Type: application/json; charset=UTF-8
Content-Length: 83

{
  "_index" : "website",
  "_type" :  "blog",
  "_id" :    "124",
  "found" :  false
}</pre>
</div>
<div class="section">
<div class="titlepage"><div><div>
<h3 class="title">
<a id="_返回文档的一部分"></a>返回文档的一部分<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elasticsearch-cn/elasticsearch-definitive-guide/edit/cn/030_Data/15_Get.asciidoc">edit</a>
</h3>
</div></div></div>
<p>默认情况下， <code class="literal">GET</code> 请求会返回整个文档，这个文档正如存储在 <code class="literal">_source</code> 字段中的一样。但是也许你只对其中的 <code class="literal">title</code> 字段感兴趣。单个字段能用 <code class="literal">_source</code> 参数请求得到，多个字段也能使用逗号分隔的列表来指定。</p>
<div class="pre_wrapper lang-sense">
<pre class="programlisting prettyprint lang-sense">GET /website/blog/123?_source=title,text</pre>
</div>
<div class="sense_widget" data-snippet="snippets/030_Data/15_Get_document.json"></div>
<p>该 <code class="literal">_source</code> 字段现在包含的只是我们请求的那些字段，并且已经将 <code class="literal">date</code> 字段过滤掉了。</p>
<div class="pre_wrapper lang-js">
<pre class="programlisting prettyprint lang-js">{
  "_index" :   "website",
  "_type" :    "blog",
  "_id" :      "123",
  "_version" : 1,
  "found" :   true,
  "_source" : {
      "title": "My first blog entry" ,
      "text":  "Just trying this out..."
  }
}</pre>
</div>
<p>或者，如果你只想得到 <code class="literal">_source</code> 字段，不需要任何元数据，你能使用 <code class="literal">_source</code> 端点：</p>
<div class="pre_wrapper lang-sense">
<pre class="programlisting prettyprint lang-sense">GET /website/blog/123/_source</pre>
</div>
<div class="sense_widget" data-snippet="snippets/030_Data/15_Get_document.json"></div>
<p>那么返回的的内容如下所示：</p>
<div class="pre_wrapper lang-js">
<pre class="programlisting prettyprint lang-js">{
   "title": "My first blog entry",
   "text":  "Just trying this out...",
   "date":  "2014/01/01"
}</pre>
</div>
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